Photographic film gate for projectors



June 8, 1948. c, TUTTLE 2,443,171

rnowocmarc mm GATE FOR PROJECTORS Filed Sept. 14, 1945 118 n I j [HF 55%A 11 114' 1 9 ymmimy 102 1 103 7 v J06 FTON M. TU TT INVENTOR 11, L5\IO3 @100 By WM film plane of the Patented June 8, 1948 rnorocmrr'nc FILMGATE Fon momc'rons Clifton M. Tuttle, Rochester, N. Y.', assignor toEastman Kodak Company,

Rochester, N. Y., a

corporation of New Jersey Application September 14, 1945, Serial No.816,296

'5 Claims. 1

The present invention relates to photographic film gates for projectionapparatus, and particularly to a gate designed to hold a film fiat inthe projector and cool the frame that is in projecting position.

In all projection apparatus it is desirable to position a film asaccurately as possible in a film plane at the focal point of aprojection lens in order to obtain the best definition possible. Withprojection apparatus using long focal length projection lenses. thisproblem is not too critical because such a lens system has a depth offocus which will tolerate a certain amount of curvature of the plane.However, with projection apparatus using short focal length projectionlens systems the problem of holding the film fiat in the gate becomesmore and more critical in order to obtain a desired definition over theentire projected frame of film.

Furthermore, in projection apparatus using a bright light source and inwhich the film is stillv in the gate for a comparatively long period (5to seconds) it is necessary to efilciently cool the frame of film in thegate to prevent it from being damaged by the heat and/or from catchingfire. It is known that prior art shows projectors having gates in whichthe film is cooled by air streams directed against the films to protectthem from the heat of a projector beam, but the prior art arrangementsare solely for cooling purposes, having nothing to do with holding thefilm fiat at the gate, and are necessarily unduly noisy because of themanner in which the airstreams are directed into the gate.

The present invention relates to a photographic film gate which isadapted for use on the photographic recorder disclosed in pending U. S.patent application Serial No. 600,250, filed June 19, 1945, and which isa decided improvement in the film gate shown in said application.

One object of the present invention is the provision of a photographicfilm gate which holds the entire frame of film fiat within a :few wavelengths of light. v

Another object is to provide a film gate in which air pressure is usedto hold the film fiat and at the same time efilciently cool the same.

, And a further object is to provide a film gate of the type describedwhich is silent in operation despite the use of air under pressure tohold the film fiat and to cool it.

And another object is to provide a film gate which is simple and ruggedin construction, despite the fact that it is most eificient inoperation,

2 and contains no movable parts which can wear out.

The novel features that I consider characteristic of my invention areset forth with particularity in the appended claims- The inventionitself, however, both as to its organization and its method ofoperation, together with additional objects and advantages thereof, willbest be understood from the following description of specificembodiments when read in connection with the accompanying drawings inwhich Fig. 1 is a side elevation of a projection apparatus incorporatinga film gate constructed in accordance with a preferred embodiment of thepresent invention,

Fig. 2 is an end elevation, partly in section, of the projectionapparatus shown in Fig. l, l

Fig. 3 is an enlarged top plan view of the film gate per se,

Fig. 4 is a longitudinal sectional view taken substantially on line 4-4of Fig. 3, and

Fig. 5 is a transverse sectional view taken substantially on line 5-5 ofFig. 4.

Like reference characters refer to corresponding parts throughout thedrawings.

Briefly, the present film gate comprises two apertured gate memberswhich when brought into race to face relation form a channel throughwhich the film strip is moved longitudinally. The base of the filmguiding channel, or at least that portion including the aperture, is atransparent plate which defines the film plane and against which thefilm strip is held fiat by air pressure. The other side of the channel,and particularly that part including the aperture in the other gatemember, is slightly spaced from the film where the latter is forcedagainst the transparent plate by air issuing from the aperture toconstitute an exhaust conduit for said air which runs lengthwise of saidgate member from said aperture and causes the exhausting air to flattenthe full width of the film in the gate with a sweeping action. Theaperture in the upper gate member is enlarged to form an air chamberwhich is closed by a window. Air under pressure is introduced into thischamber in a direction away from the open end thereof so that a uniformpressure is built up therein and the air issues over the entire open endwith substantially equal force to give the desired flattening action tothe film in the gate. 1

For purposes of disclosure I have shown my novel gate in conjunctionwith a projection apparatus of the type disclosed in the above notedcopending application for it was for this use- 69, and a deviating ofthe groove or channel that it was designed. However, it will be readilyappreciated that it could be used in any type of projection apparatuswith little or no modification.

Referring now to the drawings, and particularly to Figs. 1 and 2, thecomplete projection apparatus includes a lamphouse 58 mounted on asupporting wall 59 so that it is to one side of the film path. In thislamphouse there is positioned a lamp SI whose filament is located belowthe plane of vertical wall of the lamphouse at a point below the filmpath, and in alignment with the lamp filament, there is a mount 63containing a suitable condenser system 64 and a right angle prism 65,which in combination with a reflector 60 in the lamphouse form anoptical system for uniformly illuminating the aperture of the film gate.A second optical mount 68 is fixed to the supporting wall 59 above thefilm gate, and this mount includes a suitable projection lens system anenlarged image of the film frame in the gate and project it forwardlyonto a suitable viewing screen, not shown.

Inasmuch as a relatively bright source of illumination is needed toproject an image of the magnification desired, 360 times, along with thefact that the exposed area of film remains in the projecting positionfor a comparatively long time, means must be provided for supporting thefilm at the gate to prevent otherwise being damaged by the intense heat.Furthermore, and more important, since this desired magnification mustbe obtained with a limited projector to screen distance, it is necessaryto use acomparatively short focal length projection lens system. Thismakes it imperative that the entire frame of film in the gate remainfiat very accurately in the film plane so that definition of the entireprojected image will be satisfactory. To these ends, the novel film gateconstituting the present invention has been designed.

Referring now to the drawings, and particularly to Figs. 3, 4, and 5,the novel film gate constituting the present invention will bedescribed. The film' gate includes a first or bottom elongated gatemember I which isfixed to the mount 63 in any suitable manner, notshown, so as to guide the film across the light beam of the projector.This gate member includes a projection'aperture IOI which is in opticalalignment with the condenser system of the projector. It is alsoprovided with a channel or groove I02 running the full length thereof,see Figs. 4 and 5, which is substantially the same width as the filmstrip F moving therethrough so that it guides the same in longitudinalmovement. The bottom I02 is recessed about the aperture IIlI to providea seat for a transparent plate I03. The top surface of this platepreferably is flush with the bottom of the channel and its top surfaceshould be substantially optically fiat because it constitutes the filmplane of the projection system. It will be noticed that the top of theplate is located below the top of the gate member by an amountsubstantially the same as the thickness of the film so that the film isguided edgewise by the channel I02 and its top surface is flush with, orpreferably slightly below, the top surface of the gate member. It ispointed out that instead of having the transparent plate I03 seated in arecess in the groove of the channel of the gate member, as shown, theentire bottom of the channel could be a transparent plate if the filmpath. Fixed in the v prism 10 which in turn form mittently by anysuitable mechanism,

it from catching fire or desired. This would eliminate the precisionnecessary in forming the depth and the thickness of the plate to obtaina bottom in the channel lying in a single plane.

The film strip is held in the channel of the bottom gate member I00 by atop elongated gate member I05 of the form best shown in Figs. 3-5. Thisgate member rests on the top of the first gate member and, whenperforated film is used, preferably includes two film guides I06 ateither edge which extend bottom gate member and engage the margins ofthe film to hold the same in the channel. The film guides I06 are justwide enough to cover the perforations in the edges of the film strip forthe reasons hereinafter fully set forth. This top gate member is held inplace on the bottom gate member by having one end I01 thereof extendingthrough an aperture I08 in the supporting wall 59 while the other endthereof is held to the bottom gate member by screws I09. It is pointedout that the top gate member merely acts to confine the film strip tothe channel I02 in the bottom gate member and should not be drawn downsufficiently tight to hamper the film strip from being fed through thegate means, such as sprocket 80 which is turned internot shown.

That portion of the top gate member I05 above the aperture MI in thebottom gate member I00 is thicker than the remainder of the gate memberand includes an aperture I III in optical alignment with the apertureIOI. The inner end III of this aperture slightly smaller than, theaperture IOI in the gate member and is substantially the same size asthe frame of film in projecting position. That portion of the aperture II0 intermediate the two faces of the thick portion of the gate memberI05 is enlarged as shown at II2 to form an air chamber whichcommunicates with the inner end III of the aperture by a conical wallH3.

. the apertures IM and H0 in the gate members to permit the projectedimage of film to pass to the projection lens. This cap is fastened tothe top gate member I05 by screws H6 and a circular fiange thereonclosely fits between the edge of the window I I4 and the wall of theseat therefor to provide a fluid tight connection.

The wall of the thick portion of the gate member I05 is provided with aninlet port I H to which an airline I I8 connected to a source of airunder pressure, such as an air compressor, not shown, maybe connected tointroduce air into the inner chamber. It will be noted that this port isdirected into the air chamber at right angles tc the axis thereof, oraway from the film, so that it is not the direct stream of air therefromthat is relied upon to hold the film fiat in the gate. Instead, theconstruction of the chamber and the manner of bringing the air thereintois such that a substantially uniform pressure is built up in the chamberand a blast of air substantially the size of the inner end I II of theaperture IIO strikes the entire frame of film at right angles thereto,and serves to press the film against the transparent plate I03. It hasbeen found that by this arrangement the entire frame of film at the gateis actually held fiat within a few wave lengths of light as evidenced bythe appearance of interference ringsin the projected image.

into the channel I02 in the by any suitable is substantially the samesize as, or

air from entering the nated. In this case the under To provide anexhaust for the air and to make this exhaust serve of the top ate member7 guides I8 is cut away the full length of the gate member to provide anexhaust conduit 9 between the top gate member and the film surface.

a useful purpose, that portion I between the film Thus. air issuing fromthe air chamber must pass dult to the atmosphere to, sweep the film fiatagainst said transparent plate and cool it at the same time.

a of air under pressure.-

I03. It will be understood that if unperforated film were used that thisdifilculty would not pre sent itself and the film guides could beelimiside of the edges of the top gate member could confine the marsinsof the film to the channel member, it being assumed that the channelwould be substantially the same depth as the thickness of the film.

Another remarkable and desirable feature of this film gate is thatdespite the use of an airblast to hold the film fiat in the gate and tocool it in situ there is comparatively no noise. This is important inany projection apparatus, but it an elongated bottom is particularlyimportant in projection equipment which is not enclosed in a projectionbooth and which is used in the environment of sound recording equipmentin. connection with the projector or entirely separate therefrom. Itwill be appreciated that this gate makes possible the use of an airblast ing in a restricted 7 way, in projecting systems using short focallength projection lenses and wherein only a limited space is availablebetween the-gate andthe projection lens.

Although I have shown and described one specific embodiment of myinvention I am fully' I aware that many modifications thereof arepossible. My invention, therefore, is not to be limited to the-precisedetails and construction shown and described, but is intended to coverall modifications coming within the scope of the appended claims. 1

Having thus described claim as new and desire to secure by LettersPatent of the United States is:

1. A photographic film gate comprising a pair of elongated aperturedgate members in face to face relation a first gate member provided witha longitudinal groove substantially the width of the film strip toreceive and guide the strip longitudinally; a transparent plate in thebottom of said groove in covering relation with said aperture andconstituting the film plane; a pair of spaced film guides on said secondgate member adapted to extend into said groove in the first gate memberand engage the longitudinal margins of a film s rip therein and confinethe film to longitudinal movement therein; that the face of the myinvention, what I 3. A photographic film gate according to'cl'aim l inwhich that portion of the aperture in said second gate member spacedfrom said recessed portion is enlarged in chamber; an inlet portextending into the side wall of said chamber which is adapted to beconair under pressure.

ing film having perforated margins comprising member provided with agroove extending lengthwise thereof through which a strip of film isadapted to be fed longitudinally, said groove being substantially theto-face with the top surface of said bottom member and forming with saidgroove a channel through which the film passes and which chanfor filmflattening and coolspace; or, stating it another the side wall of saidnel is slightly deeper than the thickness of the film and is open onlyat the endsof the members remote from said projection aperture, a pairof laterally spaced elongated film guides extending downwardly from thelower face of said top member into the edges of the groove in the bottommember to engage the margins of a film situated in said groove and beingof such width as to cover the perforations in the film strip, said topmember provided projection aperture in alignment with the projectionaperture in said bottom plate, said bore including an enlarged portionspaced from said film and providing an air chamber terminating in anexit adjacent the film and which exit is smaller in diameter than saidair chamber and is' substantially the size of the exposed frames of thefilm, a transparent plate closing the upper end of said bore, and an airinlet in bore directed away from the film surface and into which air,under presthe bottom gate 5. A photographic film gate comprising a topand bottom elongated plate in face-to-face relation and each plateprovided with an aperture disposed intermediate the ends of the plateand in alignment with each other, the upper face of said bottom plateprovided with a groove substantially the same width as the film anddeeper than the thickness of the film whereby when a film is locatedtherein there exists a restricted volume to provide an air with a boreconstituting a exhaust conduit between the upper face of the film andthe lower face of the top plate from both sides of the aperture in saidtop plate to angles to the top face thereof to hold the film flat insaid film plane and must exhaust through said exhaust conduits and sweepthe film fiat against the bottom of said groove and effect a coolingthereof.

CLIFTON M. TU'I'ILE.

REFERENCES crrnn The following references are of record in the file ofthis patent:

5 UNITED STATES rxrnn'rs Number Name 7 Date 1,082,678 Casler Dec. 30,1913 1,427,575 Brenkert et a1 Aug. 29, 1922 10 1,170,659 Oehrnichen..-July 15, 1930 2,029,871 Johnson Rh. 4, 1938 2,199,305 Dewey Apr. 30,1940 2,315,914 Wengel Apr. 6,1943 1r FOREIGN PATENTS 7 Number Country IDate 297,130 Great Britain Sept. 14, 1928 331,743 Great Britain July 10,1930

